In a recent issue of a marine activity magazine, one writer recommended against using Global Positioning System (GPS) navigation equipment because, paradoxically, this system is too accurate. Many of the maps used by operators of small and medium size boats still use maps prepared by U.S. Navy and Coast Guard personnel in earlier decades when the measurement methods had estimated inaccuracies as large as hundreds of meters. Use of GPS navigation information in the open oceans and seas is not a problem, because use of this information is not tied to nearby terrestrial monuments or landmarks. However, when a boat is operating in, say, the California Delta region or on a river with many tributaries, use of nearby terrestrial monuments is natural and to be expected. If the boat operator attempts to reconcile the discrepancies between the old Navy/Coast Guard maps, visually perceptible landmarks and GPS navigation information, the operator can become disoriented.
Maps and charts have been prepared and used in connection with various location determination systems (LDSs), such as GPS, GLONASS, Loran, Tacan, Decca, Omega, VOR, DME, JTIDS, PLRS and an FM subcarrier system. DiMatteo et al, in U.S. Pat. No. 4,135,190, disclose a navigational plotter system including a geographical map with location lines prepared with the aid of a Loran or Omega LDS. Intersections of location lines with coordinate baselines located on the map are recorded in coded form for direct readout of a selected location, for tracking of location and/or movement of a vehicle or vessel across the two-dimensional surface represented by the map.
A navigation display that provides a continuous pictorial or graphical display of the present location of a movable vehicle or vessel, using an LDS such as VOR, Loran, ADF, DME or Tacan, is disclosed by Scovill in U.S. Pat. No. 4,253,150. The charts are stored on photographic film, and the portion of the film displayed is varied to include the present location. This system can be used to provide readout of present ground speed of the vehicle or vessel, bearing, and estimated time to reach a waypoint or the destination. Most of the discussion is concerned with positioning of the portion of the film displayed.
In U.S. Pat. No. 4,428,052, Robinson et al disclose a navigational aid and autopilot system that includes display of a selected portion of a chart showing the location of a vehicle or vessel being tracked. The vehicle or vessel location may be shown at the center or near an edge of the portion of the chart displayed. Water and nearby land masses may be displayed on the selected portion of the chart, as well as relevant information such as the depth of the water at a location near a land mass.
Setlift et al disclose an electronic chart system that stores and visually displays a plurality of charts or maps digitally, where the charts have been prepared using a location determination system, such as Loran, in U.S. Pat. No. 4,428,057. The visually displayed image can be compressed or expanded to meet the current needs of the viewer. Each point on the chart is given an index, indicating whether that point is "land" or "water." Navigation information, such as location and bearing for a moving object, is available.
A navigation system, including an integrated electronic display for charts or maps prepared by a location determination system such as Loran or Decca, is disclosed in U.S. Pat. No. 4,590,569, issued to Rogoff et al. A plurality of charts is stored digitally and displayed as needed, together with alphanumeric data such as location coordinates, bearing, waypoints, and estimated time before arrival at a waypoint or destination. Radar return signals are received from nearby land masses, and this information is superimposed on the stored images in some situations. If the object tracked is located off-shore, the off-shore LDS receives (Loran) offset data from a plurality of on-shore LDS monitors to periodically correct the location of the off-shore object.
U.S. Pat. No. 4,685,068, issued to Greco et al, discloses a map digitization and feature extraction system that uses pattern recognition to add editable features, such as terrain elevation, vegetation, water storage and transport facilities, and electrical communication lines, to an electronic map that is being assembled. The added features are drawn from one or more separate databases, and features of the same class can be given the same color for display. A first visual display monitor for an interim or working display and a second monitor for final display, are preferably positioned adjacent to each other. A paper map, used for feature placement or details, is cut or sectioned into rectangles of length a few km on a side, and the sections are scanned into a computer for storage and subsequent use.
Green et al disclose a method for accurately displaying location information, obtained from a Loran system, on a map in U.S. Pat. No. 4,791,572. The actual locations of various Loran antenna monuments are determined and used together with Loran data to enhance the accuracy of a location on the map, by distorting map grid lines if necessary. Reconciliation of a location shown on two different maps is not provided.
A map-aided navigation system that uses TERCOM-SITAN control signals is disclosed by U.S. Pat. No. 4,829,304, issued to Baird. An aircraft flies over terrain to be mapped and estimates aircraft location and altitude at a sequence of sampling points. These data are Kalman filtered, and the resulting filtered data are used to determine elevation and slope for this terrain. On a subsequent flight over this terrain, an aircraft uses altimeter sensing and the terrain map to determine the most likely flight path actually followed by the aircraft.
Gray et al disclose a method for accurately updating location information contained in a digital map, in U.S. Pat. No. 4,891,761. A vehicle is dispatched to a neighborhood of an unknown location, which may be a landmark that has not yet been surveyed. The vehicle moves along a segment between a known landmark, such as an already-surveyed intersection and the unknown location and transmits location information to a central station to produce an updated digital map.
A method for representing digitized image data for forming cross-sectional images of an object is disclosed by Essinger et al in U.S. Pat. No. 4,939,646. This method is useful in computer-assisted tomography, magnetic resonance imaging and other fields where three-dimensional representations are needed. A two-dimensional "slice" of a three-dimensional object is limited by a boundary curve, and image features within this curve are represented as locations in polar coordinates. A locus of points equidistant from and lying within the boundary curve is used for feature location and placement. Another method of digitizing two-dimensional sections of a three-dimensional object is disclosed by Koch in U.S. Pat. No. 5,231,470.
In U.S. Pat. No. 4,939,661, issued to Barker et al, a marine navigation system that represents locations in cells that cumulatively cover an entire region is disclosed. Only those cells that contain a portion of a coastline have much associated location data.
A vehicle navigation system that uses local topographical maps to correct an aircraft flight path is disclosed in U.S. Pat. No. 4,939,663, issued to Baird. During flight, local altitude measurements are made and used with a digital database containing local elevation (above a ground reference surface) of the Earth's surface. The location of the aircraft is sampled separately and is compared with the local elevation contour corresponding to the altimeter measurement; a location correction is determined that places the aircraft location over the elevation contour. Here, the local altitude coordinate of the aircraft is determined exclusively by the altimeter measurement, and the other two aircraft position coordinates are determined approximately by independent position sampling, which may use aircraft dead reckoning.
U.S. Pat. No. 4,982,332, issued to Saito et al, discloses a road data generating system is disclosed for use in an on-board vehicle navigation system. Locations of points on roads on a map are determined and stored, by reference of each such point to a nearest road intersection based on location data sensed by the moving vehicle. These dam are compared with any extant location data for that road, and extant data are replaced on the map by new data at a given location that are believed to be more accurate than the extant data near that location.
Dedieu et al, in U.S. Pat. No. 4,998,212, disclose a method of representing a geographical map as an assembly of curvilinear trapezoids that fit together along their common edges, in a manner that approximates sections that occur on a globe surface of the Earth. The map sections are deformed and rotated and fitted together to provide a representation of a region of interest.
A map and text display system for aircraft navigation is disclosed by Factor et al in U.S. Pat. No. 5,057,835. The system stores terrain elevation information for regions adjacent to a flight path and compares the presently measured aircraft altitude with the maximum terrain elevation for the local region over which the aircraft is positioned, to determine if the aircraft altitude is above a safety threshold for that region. Aircraft latitude, longitude and altitude are determined conventionally, and no second source of aircraft altitude information is used to vary or improve the altitude estimate.
Currin et al disclose a method for forming a composite terrain map from a mosaic of component images in U.S. Pat. No. 5,187,734. Digitized two-dimensional orthographic projections of the component images are formed, high-pass filtered and merged with a digitized, low-pass filtered overview map to form a composite map. Warping, using two-dimensional warping polynomials, is employed to map the component images onto a common set of spatial coordinates on a larger map.
In U.S. Pat. No. 5,208,757, issued to Appriou et al, an on-board system for determination of the location of an airborne vessel, such as an aircraft, is disclosed. The spatial coordinates of discrete landmarks on the terrain below are entered into a computer memory. As the vessel flies over a landmark, the known location of this landmark is used to correct the location given by another navigation means that uses images of small portions of the terrain below for location determination. Kalman filtering is applied to the location of the vessel relative to the terrain.
An interactive automated mapping system that uses location information determined using a GPS is disclosed by Mauney et al in U.S. Pat. No. 5,214,757. Attributes related to location information can be entered, stored and subsequently displayed. The system creates new maps and/or annotates existing maps but does not provide reconciliation between an existing map and a new map.
U.S. Pat. No. 5,271,066, issued to Leonard, discloses apparatus for determining two-dimensional spatial coordinates on a map, using a viewing mechanism that allows scanning and digitization of designated points on the underlying map. An associated scanner can be rotated relative to the underlying map. Another rotatable scanner for capture of image data is disclosed by Faust et al in U.S. Pat. No. 5,280,370.
Interpolation image processing of a digital map is employed to determine pixel color is disclosed in U.S. Pat. No. 5,299,300, issued to Femal et al. Interpolation of pixel color or related data, for a plurality of pixels with spatial locations adjacent to the spatial location of a target pixel, is used to compute to compute the pixel data for the target pixel.
Bormans, in U.S. Pat. No. 5,325,482, discloses a system for adding new network data to an existing electronic map, stored in memory. A new map, containing only the new data, is superimposed on the existing map, and corresponding reference points on each map are incrementally moved until they coincide. A third electronic map is then prepared, combining the existing map features with the new data features. Interpolation of reference point locations is sometimes performed.
A system for correcting a compass heading for a vehicle is disclosed in U.S. Pat. No. 5,339,246, issued to Kao. Two or more magnetic compass heading readings are sensed, and a GPS-determined compensation factor is computed to adjust a magnetic heading value to a true heading as indicated by the GPS. The magnetic compass heading and GPS heading values are referenced to a single map.
In U.S. Pat. No. 5,345,086, Bertram discloses an automatic map compilation system that extracts three-dimensional surveying or similar information from a plurality of two-dimensional maps. A pair of stereoscopic maps, showing data on terrain and/or associated altitude(s), is scanned into a computer, and altitudes for topographic sections are determined, if desired. An orthographic image projection is prepared from the scanned-in data and may be displayed as a photograph or orthophoto. Three-dimensional coordinates of a point are determined two or more from two-dimensional views.
These approaches generally assume that the accuracies of the navigation or survey system and of the map or chart agree with or are consistent with each other, if two such maps or charts are used. Many of these approaches require use of scanned-in location and/or feature information so that a physical map, on paper or another similar substrate, cannot be used directly. If the map or chart used has associated inaccuracies that are much larger than the associated inaccuracies of the navigation system used, the accuracy of monitored and/or tracked locations will be no better than that of the map or chart. The conclusions drawn from use of such a map may be misleading, in an environment having many features that appear to be similar. What is needed is an approach that allows reconciliation of a more accurate navigation system with a less accurate physical map or chart to provide increased accuracy for the combination. Preferably, the accuracy of a location shown on the physical map should improve with improvement of the accuracy of the navigation system.